POLOLU VALLEY LOOKOUT, Big Island  A pair of 'io, Hawaiian hawks, ride the air currents above 'Ako'ko'a Point, the paths of their flight weaving gracefully in and out against the light blue of the sky.

Our guide, Rob Pacheco, names them, as he has named much of the vegetation and wildlife and the geographic features we have spotted during a morning's hike along the Kohala Ditch trail in North Kohala, and in exploring Waikama Gulch and 'Opaepilau Stream, where Pacheco's Hawaii Forest & Trail Co. is carving out a new trail.

Pacheco's knowledge is impressive and eclectic, as is that of the guides he employs for other adventures, including a mule adventure, three different birdwatching tours, volcano visits and stargazing at Mauna Kea summit.

Our walk this morning is along the level, easy trail carved into the side of the ridge, 1,000 feet above Pololu Valley, which appears below as a a wide, flat landscape of pebbly beach, ironwood trees, muddy streams, marshes and thick hau forest. During World War II, the valley was used by the military to practice amphibious operations, and you can still find metal landing tracks down there, Pacheco says.

His company used to lead a hike down the public trail to Pololu Valley, but he prefers this one, with its peek-a-boo views and four waterfalls leading ultimately to dramatic Kapoloa Falls, where the trail passes behind the cascading water. The trail continues on into the wilderness, but Pacheco's outfit stops at Kapoloa.

It's a fine, clear Saturday morning. "The temperature up here is usually perfect," he says, although the area gets a great deal of rain. The path, paved with rock by ditch workers to accommodate the mules that did so much of the hauling, is lined with palapali, maidenhair, 'awapuhi, guava, waiawi, ti, hapu'u and many other plants. "I love to bring locals up here," says Pacheco, "they go crazy when they see the ti growing as high as trees."

 Honokanenui, the great gorge to the west that produces the most water for the tunnel. 'Awini, the next valley over, toward Waipi'o and Honoka'a in the far distance, where Kamehameha I was reared under the childhood name of Pai'ea. "The ditch company used to take mules in and out of these valleys every day. People used to live down there. No more," he says.

 Kalo Pololu, the crimson-stemmed variety of taro named for the valley where it used to be cultivated. "Supposed to make really good poi. Besides poi, the Chinese raised rice in the valleys in the 1800s. All gone now," he says.

 Uakea, the white mist that forms in the gulches as the waterfalls plunge violently into the ponds during times of "big water." He tells a rueful anecdote about bringing actor William Shatner up here for a TV shoot; wading into a stream for a shot, the actor lost hold of an immensely expensive camera lens and the two watched as it bumped and crashed down the tiered stream  a timely reminder to watch your step.

 Waohala, the name given to a place where a chanter could test his voice against the wind and waves. Pololu beach is such a place.

Pacheco shows us a cave that allowed workers access to the ditch, and throws a stone down the shaft so we can hear it plink into the water. "Seventeen people and who knows how many mules died digging this ditch," Pacheco explains as he bends back some branches that have encroached on the path where his company leads twice-daily three-mile hikes. He leases the rights to use the trailhead from a private landowner. His workers maintain the trail, which is state-owned, the state having taken over the ditch after the last Kohala plantation closed in 1975.

The Kohala Ditch was, and still is, an awesome feat of engineering, and Pacheco tells the story well. The famed ditch was built from 1904 to 1906 under the direction of engineer M. M. O'Shaugnessy to bring water from Honokane Stream, at 1,030 above sea level, 22 miles west to Hikapoloa, near Hawi. It passes intermittently through 17 miles of tunnels dug into the mountain by immigrant workers, mostly from Japan. They worked for a dollar a day.

Even after the ditch was built, it's upkeep was a full-time job for many. On the trail, we pass a metal plate rudely inscribed with an awl. It commemorates the team of men who built the short stone bridge on which we are walking. "Kohala Ditch Co. July 20, 1922," it says, then proudly lists builder K. Hinokawa and his four crewmen, along with the names of the Kohala Ditch Co.'s managers.

Development of the ditch was backed by rancher Samuel Parker, plantation owner John Hind and other business magnates of the day at a cost of about $600,000. (Pacheco notes that a single short flume cost $700,000 to build just seven years ago.) Kohala sugar planters who would benefit from the ditch were so skeptical about the project that they signed contracts guaranteeing to buy the water, but not providing to build the flumes that would connect their lands to the ditch, Pacheco said. Many were stuck paying for water they couldn't get their hands on.

Over the years, the ditch served many purposes beyond its intended one of watering 13,000 acres of sugar lands, such as being a means of transporting 'okolehau (moonshine liquor) to customers from stills hidden in 'Awini Valley. Now it's the center of a couple of tourist attractions  not just this hike, but also a kayak flume-riding operation that's extremely popular.

Pacheco, who grew up in California and whose Portuguese ancestors once lived in the Islands, has plans to develop a family-friendly loop hike with a waterfall swim on pasturelands near Pololu Lookout. The Kohala Ditch trail hike he leads is a bit chancy for small children; although it's flat, it is narrow in places, and the drop is heart-stoppingly steep.

"People just want to bathe in a waterfall. It's a fantasy they have," he says. His goal is to fulfill those fantasies in a responsible, culturally sensitive way.

Our morning's hike, which ends with a refreshing tailgate picnic of fresh fruit and cool water at the mule station near Pololu Lookout, certainly fulfilled our fantasy of spending some time in a natural setting and learning more about Hawai'i's plantation-era history.